This invention relates to oil and gas well casing hanger apparatus, and in particular to a mudline casing hanger assembly for supporting the casing at the mudline of a subsea well.
In such an apparatus commonly known as the mudline suspension system, a plurality of strings of casing are concentrically located, each one being supported within the successively outer one at the mudline. Each casing string which runs from the hanger downwardly is matched by an upward extension or conductor passing to the surface platform. Such a system is characterized by the severe limitation of annular space through which to run a hanger for support from the next adjacent hanger body.
This problem of landing a casing hanger inside another casing hanger has led to a number of solutions with respect to collapsing and expanding load transferring devices. They have generally been resilient devices such as "C" rings which in the relaxed condition are expanded. These are then held in, and pulled down by various retaining rings and shear pins, so that they may enter the casing and be pulled down through the blowout preventer and casing to the hanger position.
Many of these devices require considerable machining, and some are not susceptible to being recocked should they inadvertently come loose during running, or for lifting the string for reciprocation. Some have limitations on retrieval should there be a need to lift the casing string after setting the hanger.